1. Field of the Invention
The present invention relates to a device for the stabilization of the spine comprising at least two pedicle screws and at least one interjacent linking member. The present invention further relates to pedicle screws possessing a movable ball element in a movable screw head for easier introduction of the linking member, this construction providing an optimal reducibility of the vertebrae while strongly enclosing the linking member.
2. Description of Related Art
In the state of the art, only embodiments which describe a support of the linking member in the screw head of the pedicle screw along the axial axis, which provides a certain flexibility even after the implantation, are known.
Thus, US 2003/0220642 A1 discloses in one embodiment an elastic linking member with a thread and associated pedicle screws with screw heads disposing of a respective thread, so that the linking member can be introduced into the screw heads by rotational movements and is movable along its longitudinal axis.
EP 0 669 109 B1 describes a support device for the spine, which allows less a movement of the linking member along its longitudinal axis than rather a movement of the individual pedicle screws relative to each other. For this purpose, a flexible strip is used as the linking member, and a slightly deformable support element is attached to the strip, wherein the support element abuts on the screw heads of two pedicle screws, respectively.
U.S. Pat. No. 6,761,719 B2 discloses a support device for the spine which allows movements by inserting a shape memory metal as a linking member between the vertebrae which possesses pseudoelastic properties at body temperature.
The embodiments referred to in WO 03/037216 A2 attempt to achieve a flexibility of the linking member by using a flexible linking member which is made for example of polyester, polyethylene, polylactide, or nitinol, and which is fixed in the screw heads of the pedicle screws and possesses absolutely no degrees of freedom of movement within the same.